(1) Field of the Invention
The present invention relates to a process for producing beryllium-copper alloys having excellent mechanical strength, electric conductivity, reliability, etc. The invention also relates to beryllium-copper alloys produced by the above process.
(2) Related Art Statement
Beryllium-copper alloys composed mainly of Be and Cu have been widely used as as high strength spring materials, electrically conductive materials, etc. Beryllium-copper alloy is ordinarily converted to a thin sheet by conventional processes as shown in FIG. 2, for example. A beryllium-copper alloy having a given composition is cast, the cast beryllium-copper alloy is hot rolled, the hot rolled alloy is worked to a given dimension by subjecting it to annealing and cold rolling to remove work hardening, and finally, the cold rolled sheet is finished by solid solution treatment.
The annealing effected midway is carried out by strand annealings in which the alloy is recrystallized at high temperatures not lower than 800.degree. C. for a short time period, and the alloy is subjected to the solid solution treatment to soften the alloy. Further, no conventional knowledge is available regarding the reduction rate in the cold rolling which is carried out between a plurality of intermediate annealing steps, and such a reduction rate has been merely set by expediency. The term "reduction rate" (%) equals (thickness before rolling--thickness after rolling)/(thickness before rolling).times.100 with respect to the alloy.
However, the process for producing the beryllium-copper alloy shown by the flow chart in FIG. 2 has the following problems.
(1) Variations are likely to occur in alloy characteristics since the annealing is effected at high temperatures for a short time period and a recrystallization grain-growing speed is high. Therefore, since variations are likely to occur in the grain size and since the treatment is effected for a short time, a non-uniform texture after the hot rolling is difficult to eliminate. PA1 (2) It is difficult to control the average crystalline grain diameter of the final product. This is because when the grain size is controlled to obtain desired characteristics, the grain size must be controlled only by the final solid solution treatment in the case of intermediate annealing effected at high temperatures. PA1 (3) There is a high possibility that extremely duplex microstructure is produced. This is because when the temperature of the final solid solution treatment is controlled to increase the grain size, the temperature of the final solid solution treatment needs to be raised, which is likely to produce the duplex microstructure.
As discussed above, the conventional process has problems in a desired average grain size and grain size uniformity which greatly influence various characteristics, particularly, reliability. Accordingly, beryllium-copper alloys having excellent characteristics cannot be obtained.